31 August 2005Planetark / Reuters
The ozone layer has stopped shrinking but it will take decades to start recovering, US scientists reported on Tuesday.
They said an international agreement to limit production of ozone-depleting chemicals has apparently worked, but the damage to ozone has not been halted completely.
An analysis of satellite records and surface monitoring instruments shows the ozone layer has grown a bit thicker in some parts of the world, but is still well below normal levels, the scientists report in Wednesday's issue of the Journal of Geophysical Research.
Elsewhere, the decline in ozone levels has stabilized, said Betsy Weatherhead, a researcher at the University of Colorado at Boulder and the National Oceanic and Atmospheric Administration. "The observed changes may be evidence of ozone improvement in the atmosphere," she said in a statement.
The experts credited, at least in part, the 1987 Montreal Protocol which was ratified by more than 180 nations and set legally binding controls for on the production and consumption of ozone-depleting gases containing chlorine and bromine.
The prime suspects in ozone destruction are chlorofluorocarbons, or CFCs, once commonly used in refrigeration, air conditioning and industrial cleaning.
"These early signs indicate one of the strongest success stories of international cooperation in the face of an environmental threat," said NOAA administrator Conrad Lautenbacher.
Weatherhead noted that methane levels, water vapor and air temperatures will continue to affect future ozone levels.
"Even after all chlorine compounds are out of the system, it is unlikely that ozone levels will stabilize at the same levels," she said.
"Chemicals pumped into Earth's atmosphere decades ago still are affecting ozone levels today," said Sherwood Roland of the University of California Irvine. "This problem was a long time in the making, and because of the persistence of these chlorine compounds, there is no short-term fix."
The ozone layer remains so thin that cancer-causing ultraviolet radiation is still getting through.
"This study provides some very encouraging news," said Mike Repacholi of the World Health Organization. "But the major cause of skin cancer is still human behavior, including tanning and sunburns that result from a lack of proper skin protection."
